✨ Add basic .deb generation support
WiX and RPM support is still needed for verification
⬆️ Upgrade minimum CMake version to 3.14
⬆️ Upgrade Catch to Catch v2.9.2
📌 Pin Catch to v2.9.1
👷 Update .travis.yml build matrix
👷 Update .appveyor build script
✅ Update tests to be separated by file
Enable use of `tl::optional<T>` purely as a library with CMake's
`add_subdirectory`. The default configuration works are before.
* `OPTIONAL_ENABLE_TESTS` make building tests optional, enabled by default
* `OPTIONAL_ENABLE_DOCS` make building documentation optional, enabled by default